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Testing a new board PA


 

HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp current draw when hallooo'ing into the mic I had to crank R136 all the way. In that way I could get 5 watts out but only if running higher PA voltages.

I got a second board and was playing with it yesterday. I wanted to see if it behaved differently. So I hooked up the PWR, PA PWR and a mic. I get about 127mA at idle but no increase when I halloo. Does the VFO need to be connected? I'm guessing so but just thought I'd ask. That takes a little more doing and I was just curious.

Thanks!

Jonathan - KK6RPX


Vince Vielhaber
 

You only need the VFO if you want to transmit or receive. Without it
you're only saying HALLOOO to the board. :)

Vince.

HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp
current draw when hallooo'ing into the mic I had to crank R136 all the
way. In that way I could get 5 watts out but only if running higher PA
voltages.

I got a second board and was playing with it yesterday. I wanted to see
if it behaved differently. So I hooked up the PWR, PA PWR and a mic. I
get about 127mA at idle but no increase when I halloo. Does the VFO need
to be connected? I'm guessing so but just thought I'd ask. That takes a
little more doing and I was just curious.

Thanks!

Jonathan - KK6RPX



--
Michigan VHF Corp.


 

No VFO - No output!

At 19/06/2017, you wrote:
HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp current draw when hallooo'ing into the mic I had to crank R136 all the way. In that way I could get 5 watts out but only if running higher PA voltages.

I got a second board and was playing with it yesterday. I wanted to see if it behaved differently. So I hooked up the PWR, PA PWR and a mic. I get about 127mA at idle but no increase when I halloo. Does the VFO need to be connected? I'm guessing so but just thought I'd ask. That takes a little more doing and I was just curious.

Thanks!

Jonathan - KK6RPX


 

Thanks!

On 6/19/2017 8:28 PM, Raj vu2zap wrote:
No VFO - No output!

At 19/06/2017, you wrote:
HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp current draw when hallooo'ing into the mic I had to crank R136 all the way. In that way I could get 5 watts out but only if running higher PA voltages.

I got a second board and was playing with it yesterday. I wanted to see if it behaved differently. So I hooked up the PWR, PA PWR and a mic. I get about 127mA at idle but no increase when I halloo. Does the VFO need to be connected? I'm guessing so but just thought I'd ask. That takes a little more doing and I was just curious.

Thanks!

Jonathan - KK6RPX



 

Jonathan, radios amplify and modulate radio frequency (RF) signals,
that RF signal is generated by the local oscillator (LO) in this case
a synthesized VFO.
Without it you don't have anything to modulate or amplify, no RF, no
radio. This doesn't work like an audio amplifier to see your voice
output from the PA.
I hope this help you understand why that test didn't worked.
73! Dan.

On Mon, Jun 19, 2017 at 10:50 PM, Jonathan Peakall
<jpeakall@...> wrote:
Thanks!

On 6/19/2017 8:28 PM, Raj vu2zap wrote:

No VFO - No output!

At 19/06/2017, you wrote:

HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp
current draw when hallooo'ing into the mic I had to crank R136 all the way.
In that way I could get 5 watts out but only if running higher PA voltages.

I got a second board and was playing with it yesterday. I wanted to see
if it behaved differently. So I hooked up the PWR, PA PWR and a mic. I get
about 127mA at idle but no increase when I halloo. Does the VFO need to be
connected? I'm guessing so but just thought I'd ask. That takes a little
more doing and I was just curious.

Thanks!

Jonathan - KK6RPX







 

Could be due to any or many of the following reasons:

1: Low audio drive - very likely (I use an amped Motorola mic and it goes up to 10W)

2: Low VFO or BFO levels

3: BFO frequency may need tweaking to suit the filter or your voice.

4: Low BiDi amp stage gain - unlikely

5: Low gain in final RF amp stages - short out R131 and see

Considering you get 5W it is not really low as you think!

Cheers
Raj

At 19/06/2017, you wrote:
HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp current draw when hallooo'ing into the mic I had to crank R136 all the way. In that way I could get 5 watts out but only if running higher PA voltages.

xxx snip xxx

Thanks!

Jonathan - KK6RPX


 

Raj,

Thanks. Low mic gain might be it, but I thought you should get 5W out of the simple electret mic included?

And the issue is that I have to crank R136 fully over to get the 5 watts. I will short out R131 and see what happens.

JOnathan

On 6/19/2017 10:43 PM, Raj vu2zap wrote:
Could be due to any or many of the following reasons:

1: Low audio drive - very likely (I use an amped Motorola mic and it goes up to 10W)

2: Low VFO or BFO levels

3: BFO frequency may need tweaking to suit the filter or your voice.

4: Low BiDi amp stage gain - unlikely

5: Low gain in final RF amp stages - short out R131 and see

Considering you get 5W it is not really low as you think!

Cheers
Raj

At 19/06/2017, you wrote:
HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp current draw when hallooo'ing into the mic I had to crank R136 all the way. In that way I could get 5 watts out but only if running higher PA voltages.

xxx snip xxx

Thanks!

Jonathan - KK6RPX



 

Jonathan, I would consider 5W within limits.

Let me tell you a condensed story!

My Ft757Mk2 was on 10M CW. Nice pileup. Then I heard a bad tone so I gave him a T5 and he did the same. I shut down.
I opened the rig and probed and all was fine. The rig did the same after some time.
I finally realized that the PLL lost lock and was creating noise hunting for a lock.
I found the signal in the feedback loop was low when board was hot.
I figured that the loop gain was low. I just swapped some 2SC535 as I remember from other parts of the rig and
Problem solved.

Sometimes a combination of semiconductor parts results in such situations! If everything works then we don't learn anything new!

Cheers
Raj

At 20/06/2017, you wrote:
Raj,

Thanks. Low mic gain might be it, but I thought you should get 5W out of the simple electret mic included?

And the issue is that I have to crank R136 fully over to get the 5 watts. I will short out R131 and see what happens.

JOnathan

On 6/19/2017 10:43 PM, Raj vu2zap wrote:
Could be due to any or many of the following reasons:

1: Low audio drive - very likely (I use an amped Motorola mic and it goes up to 10W)

2: Low VFO or BFO levels

3: BFO frequency may need tweaking to suit the filter or your voice.

4: Low BiDi amp stage gain - unlikely

5: Low gain in final RF amp stages - short out R131 and see

Considering you get 5W it is not really low as you think!

Cheers
Raj

At 19/06/2017, you wrote:
HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp current draw when hallooo'ing into the mic I had to crank R136 all the way. In that way I could get 5 watts out but only if running higher PA voltages.

xxx snip xxx

Thanks!

Jonathan - KK6RPX


 

Oh, I forgot to mention, that is with 24V on the PA.

My plan is to get the new board up and running and then I can compare the voltages etc. between the two and try to figure it out. And no, I don't mind a bit, I have a lot to learn.

On 6/20/2017 7:51 AM, Raj vu2zap wrote:
Jonathan, I would consider 5W within limits.

Let me tell you a condensed story!

My Ft757Mk2 was on 10M CW. Nice pileup. Then I heard a bad tone so I gave him a T5 and he did the same. I shut down.
I opened the rig and probed and all was fine. The rig did the same after some time.
I finally realized that the PLL lost lock and was creating noise hunting for a lock.
I found the signal in the feedback loop was low when board was hot.
I figured that the loop gain was low. I just swapped some 2SC535 as I remember from other parts of the rig and
Problem solved.

Sometimes a combination of semiconductor parts results in such situations! If everything works then we don't learn anything new!

Cheers
Raj

At 20/06/2017, you wrote:
Raj,

Thanks. Low mic gain might be it, but I thought you should get 5W out of the simple electret mic included?

And the issue is that I have to crank R136 fully over to get the 5 watts. I will short out R131 and see what happens.

JOnathan

On 6/19/2017 10:43 PM, Raj vu2zap wrote:
Could be due to any or many of the following reasons:

1: Low audio drive - very likely (I use an amped Motorola mic and it goes up to 10W)

2: Low VFO or BFO levels

3: BFO frequency may need tweaking to suit the filter or your voice.

4: Low BiDi amp stage gain - unlikely

5: Low gain in final RF amp stages - short out R131 and see

Considering you get 5W it is not really low as you think!

Cheers
Raj

At 19/06/2017, you wrote:
HI All,

My original BITX never "aligned" correctly. In order to get the 1 amp current draw when hallooo'ing into the mic I had to crank R136 all the way. In that way I could get 5 watts out but only if running higher PA voltages.

xxx snip xxx

Thanks!

Jonathan - KK6RPX